A diorganopolysiloxane which has a functional group at only one end of the molecular chain can be copolymerized with organic monomer by utilizing the reactivity of the functional group. The siloxane is a useful modifier of the organic resins since it can impart characteristics of organopolysiloxane, such as weather resistance, surface water repellent characteristics, lubricity and as permeability to the organic resin.
A manufacturing method for the preparation of such a diorganopolysiloxane having a functional group at only one end of the molecular chain has been proposed wherein cyclic trisiloxane is subjected to a nonequilibrium polymerization reaction with alkyl lithium, or lithiumsilanolate, as the polymerization initiator, either in the presence or absence of organosilane or organosiloxane which is capped at one end with hydroxyl group and acts as a molecular weight regulator. This nonequilibrium polymerization reaction is terminated by the addition of acid or organo functional group-containing organochlorosilane (refer to JP (Kokai) 59.78236, JP (Kokai) 1-131247, JP (Kokai) 2-92933). However, when the diorganopolysiloxane having a functional group at only one end of the molecular chain obtained by this manufacturing method is copolymerized with organic monomer, there have been such problems as the drastic increase of viscosity during the reaction. In particular, even gelation can occur when the diorganopolysiloxane has molecular weight greater than 10,000. Furthermore, unreacted organopolysiloxane remains after the reaction. In order to study the cause of these problems, the present inventor analyzed such diorganopolysiloxanes having a functional group at only one end of the molecular chain by gel permeation chromatography. It was confirmed that, in addition to the primary peak attributable to such diorganopolysiloxane having a functional group at only one end of the molecular chain, a secondary peak was observed on the higher molecular weight side of the primary peak. Further, the proportion of this secondary peak increased with increasing molecular weight of the diorganopolysiloxane having a functional group at only one end of the molecular chain. It was concluded from these results that the diorganopolysiloxane obtained by the manufacturing method described above contains diorganopolysiloxane having functional groups at both ends and diorganopolysiloxane having functional group at neither end as impurities. Consequently, a manufacturing method for preparing diorganopolysiloxane having a functional group at only one end of the molecular chain of high purity, without forming these by-products, is needed.
The present inventor previously proposed a manufacturing method of diorganopolysiloxane having a functional group at only one end of the molecular chain wherein the nonequilibrium reaction is carried out after a small amount of silanol group-containing impurities existing in the cyclic trisiloxane, used as the raw material of polymerization, are silylated in advance. This method has been effective to inhibit the secondary production of diorganopolysiloxane having functional groups at both ends caused by the silanol group-containing impurities in the cyclic trisiloxane. However, it has not been possible by this method to completely inhibit the secondary production of diorganopolysiloxane having functional group at neither end or diorganopolysiloxane having functional groups at both ends caused by the dimerization or equilibration reaction of .alpha.-hydroxydiorganopolysiloxane, which occurs as the side reaction during the polymerization of cyclic trisiloxane.